Journal of Advances in Biology & Biotechnology

Multidrug-resistant (MDR) Enterobacteriaceae recovered from clinical specimens are important contributors to the global burden of antimicrobial resistance. This study evaluated the in vitro inhibitory potential of six commercially available probiotic formulations (P01–P06) against eight clinical Enterobacteriaceae isolates recovered from pus, blood, urine and stool specimens, together with six antibiotic-susceptible comparator isolates (N01–N06). Antibiotic susceptibility was determined by disc diffusion against ampicillin, ciprofloxacin, gentamicin, cefotaxime, ceftazidime and meropenem, representing five antimicrobial classes because cefotaxime and ceftazidime belong to the same third-generation cephalosporin class. Organism-specific CLSI M100-Ed34 (2024) criteria were applied. Five of the eight clinical isolates (E02, E03, E04, E05 and E07) met the MDR criterion of non-susceptibility in at least three of five classes; E01, E06 and E08 were classified as non-MDR and combined with N01–N06 to form a nine-isolate non-MDR panel. Cell-free supernatants of each formulation were tested in triplicate by agar well diffusion. At the isolate level, mean inhibition zones against the MDR panel ranged from 8.44 ± 0.56 mm (P01) to 15.56 ± 0.60 mm (P06), whereas the corresponding means against the non-MDR panel ranged from 10.23 ± 1.03 mm to 16.82 ± 1.10 mm, representing 5.2–17.5% lower inhibition in the MDR panel. Welch two-sample t-tests showed significant MDR versus non-MDR differences for P01 (p = 0.001), P02 (p = 0.002), P04 (p = 0.001) and P06 (p = 0.017), but not for P03 (p = 0.070) or P05 (p = 0.057). The correlation between resistance burden and mean probiotic-derived inhibition was negative but not statistically significant (r = −0.55, p = 0.157, n = 8) and is therefore considered exploratory. The findings provide an isolate-level in vitro screening dataset while emphasising that the present study does not establish clinical or adjunct-therapeutic usefulness.